kraken: utils: add 'StrongType'

I foresee the need to disambiguate a lot of `int`s.

src/CMakeLists.txt

@@ -2,6 +2,7 @@ add_executable(kraken kraken.cc)
 target_link_libraries(kraken PRIVATE common_options)
 
 add_subdirectory(csv)
+add_subdirectory(utils)
 
 target_link_libraries(kraken PRIVATE
   csv

src/utils/CMakeLists.txt

@@ -0,0 +1,3 @@
+add_library(utils INTERFACE
+  strong-type.hh
+)

src/utils/strong-type.hh

@@ -0,0 +1,18 @@
+#pragma once
+
+namespace kraken::utils {
+
+/// A very simple strong type wrapper.
+template <typename T, typename Tag>
+struct StrongType {
+    explicit StrongType(T value) : value_(value) {}
+
+    explicit operator T() const {
+        return value_;
+    }
+
+private:
+    T value_;
+};
+
+} // namespace kraken::utils